Classifications

• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
  • H02M1/00—Details of apparatus for conversion
  • H02M1/32—Means for protecting converters other than automatic disconnection
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
  • H02M3/00—Conversion of dc power input into dc power output
  • H02M3/02—Conversion of dc power input into dc power output without intermediate conversion into ac
  • H02M3/04—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters
  • H02M3/10—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
  • H02M3/145—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
  • H02M3/155—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
  • H02M3/156—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
  • H05K7/00—Constructional details common to different types of electric apparatus
  • H05K7/20—Modifications to facilitate cooling, ventilating, or heating
  • H05K7/2089—Modifications to facilitate cooling, ventilating, or heating for power electronics, e.g. for inverters for controlling motor
  • H05K7/20945—Thermal management, e.g. inverter temperature control
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
  • H02M1/00—Details of apparatus for conversion
  • H02M1/32—Means for protecting converters other than automatic disconnection
  • H02M1/327—Means for protecting converters other than automatic disconnection against abnormal temperatures

Definitions

• the present invention relates to a voltage converter for converting DC power from a DC power source into DC power having a different voltage value by switching operation of a switching element and outputting the same.
• the voltage converter according to Patent Document 1 is a DC battery from a secondary battery (DC power supply).
• a capacitor may be provided in parallel with the DC power supply (secondary battery) on the input side.
• the DC power supply secondary battery
• a ripple component is generated in the current flowing through the reactor.
• the current flowing through the reactor is the current of the DC power supply (DC component) ) Is superimposed with the current of the capacitor for ripple (ripple component). This suppresses current fluctuations in the DC power supply.
• the switching element generates heat during the switching operation of the switching element, and the higher the switching frequency, the greater the amount of heat generated by the switching element. Therefore, in order to prevent overheating of the switching element (transistor), the switching frequency (carrier frequency) of the switching element is changed. For example, when the temperature of the switching element is higher than a predetermined temperature, the temperature increase of the switching element is suppressed by lowering the switching frequency of the switching element.
• the filter capacitor is provided in parallel with the DC power supply, if the switching frequency of the switching element is lowered, the ripple current flowing through the filter capacitor also increases, and the temperature rise due to the ripple current of the filter capacitor increases. Increases and easily overheats.
• the temperature rise characteristics of the switching element and the temperature rise characteristics of the reactor and the filter capacitor are opposite to the change in switching frequency. Therefore, even if the switching frequency of the switching element is changed according to the temperature of the switching element to suppress the overheating of the switching element, the filter capacitor cannot prevent the reactor from overheating.
• An object of the present invention is to provide a voltage converter that can prevent overheating of a capacitor provided in parallel with a DC power source on the input side of a DC-DC converter or a reactor of a DC-DC converter. .
• the voltage conversion device includes a reactor capable of temporarily storing energy according to a direct current from a direct current power supply, and a switching element, and uses the energy stored in the reactor, from the direct current power supply.
• DC-DC converter that converts the DC power to DC power with different voltage values by switching operation of the switching element, and a capacitor provided in parallel with the DC power supply on the input side of the DC-DC converter
• a cooling unit that cools the DC-DC converter with the refrigerant
• a voltage conversion device comprising: a refrigerant temperature detection unit that detects the temperature of the refrigerant, and both the temperature of the refrigerant and the temperature of the switching element Based on the switching frequency setting section for setting the switching frequency of the switching element, and the switching element at the set switching frequency.
• a switching control unit for controlling the voltage conversion ratio of the DC-DC comparator overnight by controlling the switching operation of the child.
• the switching frequency setting unit determines the switching frequency of the switching element based on the temperature of the switching element, the first frequency, or When the second temperature lower than the first frequency is set and the refrigerant temperature detected by the refrigerant temperature detection unit is higher than the set temperature T1, the switching frequency of the switching element is set to the switching element. It is preferable to set the first frequency regardless of the temperature.
• the switching control unit when the temperature of the refrigerant detected by the refrigerant temperature detection unit is higher than the set temperature T 2 (T 2> T 1), the switching control unit sets the temperature of the refrigerant to the set temperature ⁇ It is preferable to control the switching operation of the switching element so as to lower the voltage conversion ratio of the DC-DC converter than in the case of 2 or less. In this aspect, the switching control unit preferably prohibits the switching operation of the switching element when the refrigerant temperature detected by the refrigerant temperature detection unit is higher than the set temperature T 3 (T 3> T 2). It is.
• the switching control unit prohibits the switching operation of the switching element when the temperature of the refrigerant detected by the refrigerant temperature detection unit is higher than the set temperature ⁇ 3 ( ⁇ 3> ⁇ 1). Is preferred.
• the switching frequency setting characteristic determined from the temperature of the switching element is different from the switching frequency setting characteristic determined from the refrigerant temperature.
• the voltage converter according to the present invention includes a reactor capable of temporarily storing energy according to a DC current from a DC power supply and a switching element, and uses the energy stored in the reactor to generate a DC DC-DC converter that converts DC power from the power source into DC power of different voltage values by switching operation of the switching element, and DC-DC converter is installed in parallel with the DC power source at the input side of DC-DC converter
• a voltage conversion device comprising: a condenser; and a cooling unit that cools the DC-DC comparator overnight with a refrigerant. Based on the temperature of the switching element, the switching frequency of the switching element is set to the first frequency, Or a switching frequency setting unit for setting a second frequency lower than the first frequency, and a switching element with the set switching frequency.
• a switching control unit that controls the voltage conversion ratio of the DC-DC converter by controlling the switching operation of the DC-DC converter, and a refrigerant temperature detection unit that detects the temperature of the refrigerant.
• the switching control unit is detected by the refrigerant temperature detection unit. Temperature of the cooled refrigerant When the temperature is higher than the set temperature T2, the switching operation of the switching element is controlled so as to lower the voltage conversion ratio of the DC-DC converter than when the temperature of the refrigerant is lower than the set temperature ⁇ 2.
• the voltage converter according to the present invention includes a reactor capable of temporarily storing energy according to a DC current from a DC power supply and a switching element, and uses the energy stored in the reactor to generate a DC DC-DC converter that converts DC power from the power source into DC power of different voltage values by switching operation of the switching element and outputs it in parallel with the DC power source on the input side of the DC-DC comparator
• a voltage conversion device comprising: a condenser; and a cooling unit that cools the DC—DC comparator overnight with a refrigerant. Based on the temperature of the switching element, the switching frequency of the switching element is set to the first frequency, Alternatively, a switching frequency setting unit that sets the second frequency lower than the first frequency, and a switch at the set switching frequency.
• a switching control unit that controls the switching operation of the element to control the voltage conversion ratio of the DC-DC converter, and a refrigerant temperature detection unit that detects the temperature of the refrigerant.
• the switching control unit is a refrigerant temperature detection unit. If the detected temperature of the refrigerant is higher than the set temperature T3, the gist is to prohibit the switching operation of the switching element.
• the cooling unit cools either the reactor or the condenser with a refrigerant.
• FIG. 1 is a diagram showing a schematic configuration of an electric motor drive system including a voltage conversion device according to an embodiment of the present invention.
• FIG. 2 is a diagram showing a schematic configuration of an electric motor drive system including the voltage conversion device according to the embodiment of the present invention.
• FIG. 3 is a block diagram showing a configuration example of the electronic control unit.
• FIG. 4 is a diagram for explaining an example of a method for generating a switching control signal for the DC-DC comparator.
• FIG. 5 is a flowchart explaining the processing executed by the electronic control unit.
• FIG. 6 is a flowchart illustrating the processing executed by the electronic control unit.
• FIG. 7 is a flowchart for explaining processing executed by the electronic control unit.
• FIG. 8 is a diagram for explaining the operation of the voltage converter according to the embodiment of the present invention.
• FIG. 9 is a diagram for explaining the operation of the voltage-voltage converter according to the embodiment of the present invention.
• FIG. 1 is a diagram showing a schematic configuration of an electric motor drive system including a voltage conversion device according to an embodiment of the present invention.
• the electric motor drive system according to the present embodiment can be used, for example, in a vehicle drive system.
• the secondary battery 31 as a chargeable / dischargeable DC power source and the DC power from the secondary battery 31 are shown.
• DC—DC converter 3 -2 that converts DC power to DC voltage with a different voltage value, fill capacitor C 1 provided on the input side of DC—DC converter 32, and DC—DC converter 32
• Inverter 34, 36 that converts DC power to AC and outputs, and smoothing capacitor C 2 provided on the input side (output of DC—DC converter 32) of inverter 34, 36, It is equipped with a motor generator 38, 39 that can be driven to rotate by receiving AC power from Imper 34, 36, and an electronic control unit 40 that controls the entire system.
• the DC-DC converter 32 has two transistor transistors (switching elements) Q l connected in series so that they are on the source side and sink side of the positive side line PL and negative side line SL of the inverters 34 and 36. , Q2 and two diodes D1 and D2 connected in reverse parallel to the power transistors Q1 and Q2, respectively, and one end connected to one end (positive terminal) of the secondary battery 31 and the other end Is the power transistor Q l, Q Reactor L connected to the connection point of 2. Power transistor Q 1 is placed between the other end of reactor L and the output end of DC-DC converter 32 (positive line PL of inverter 34, 36).
• Power transistor Q 2 is connected to reactor L It is arranged between the other end and the other end (negative terminal) of the secondary battery 31.
• this DC-DC converter 32 when the transistor Q2 is turned on, a short circuit is formed that connects the secondary battery 31, the reactor L, and the power transistor Q2, and the reactor according to the direct current flowing from the secondary battery 31 is formed. Energy is temporarily stored in L.
• the power transistor Q 2 when the power transistor Q 2 is turned off from on, the energy stored in the reactor L is stored in the smoothing capacitor C 2 via the diode D 1.
• the DC voltage of the smoothing capacitor C 2 (DC—DC converter 32 output voltage) should be higher than the DC voltage of the secondary battery 3 1 (DC—DC converter 32 input voltage). Can do.
• the DC-DC converter 32 converts the input DC power from the secondary battery 31 to DC power with a different voltage value by the switching operation that drives the power transistors Q l and Q 2 on and off (step-up) It can function as a boost converter that outputs to inverters 34 and 36.
• the secondary battery 31 can be charged by the DC-DC converter 32 using the charge of the smoothing capacitor C2, and in this case, it functions as a step-down converter.
• a filter capacitor C1 is provided in parallel with the secondary battery 31. More specifically, one end of the filter capacitor C 1 is connected to the positive terminal of the secondary battery 31 and one end of the reactor L, and the other end of the filter capacitor C 1 is the negative terminal of the secondary battery 31. It is connected to the.
• ripple components are generated in the current flowing through reactor L.
• Inverter 34 includes a plurality of (three in FIG. 1) arms 62, 64, 66 connected in parallel between the positive line PL and the negative line SL.
• Arm 62 is A pair of power transistors (switching elements) Ql l and Q 12 connected in series between the positive line PL and the negative line SL and anti-parallel connection to each of the power transistors Q 1 1 and Q 12 Includes a pair of diodes D 1 1 and D 12.
• arm 64 is antiparallel to a pair of power transistors Q13 and Q14 connected in series between positive line PL and negative line SL, and power transistors Q1 and Q14, respectively.
• Arm 66 includes a pair of connected power transistors Q 15 and Q 16 connected in series between positive line PL and negative line SL.
• the coil (three-phase coil) 38U, 38 V, 38W of the motor generator 38 is Y (star) connected and connected to the midpoint of each arm 62, 64, 66.
• the Imper 34 converts the input DC power from the DC-DC converter 32 into three-phase alternating current with 120 ° phase difference by switching operation of the power transistors Q 1 1 to Q 16 38 3 phase coil 38 U, 38 V, 38 W. As a result, the motor generator 38 can be driven to rotate.
• the inverter 34 can convert the AC power of the three-phase coils 38U, 38 V, 38 W of the motor generator 38 into DC and supply it to the DC-DC converter 32.
• Inver evening 36 has the same configuration as Inver evening 34, including arm 72 including power transistors Q 21 and Q 22 and diodes D 21 and D 22, power transistors Q 23 and Q 24 and diode D 23, Arm 74 including D 24 and arm 76 including diodes D 25 and D 26 and diodes D 25 and D 26.
• Y (Star)
• the three-phase coil 39 U, 39 V, 39 W of the connected generator 39 is connected to the midpoint of each arm 72, 74, 76, respectively.
• Inverter 36 also uses the switching operation of power transistors Q21 to Q26 to convert the input DC power from DC-DC converter 32 into a three-phase AC that is 120 degrees out of phase, and motor generator 39 By supplying to the phase coils 39 U, 39 V, 39 W, the motor generator 39 can be driven to rotate.
• the three-phase coil of the motor generator 39 in this Inverter 36 It is also possible to convert 39 U, 39 V, 39 W AC power to DC and supply it to the DC-DC converter 32.
• filter capacitor C1 DC—DC converter 32
• the casing 42 here is made of a conductive material such as metal (for example, aluminum), so that the electronic component housed inside is also shielded from the outside.
• the casing 42 is formed with a refrigerant channel 44 through which a coolant such as a coolant (cooling water) flows as a cooling part.
• the DC-DC converter 32 (reactor, single transistor Ql, Q2) accommodated in the casing 42 can be cooled by the coolant flowing through the refrigerant flow path 44. Further, the cooling fluid flowing through the cooling medium flow path 44 allows the filter capacitor C 1, the inverter 34 (power transistors Q 1 1 to Q 16), and the inverter 36 (power The transistors Q21 to Q26) can also be cooled.
• the temperature sensor 52 is provided on, for example, a chip on which the power transistors Q 1 and Q 2 are formed, and detects the temperature T t of the power transistors Q l and Q 2.
• the temperature sensor 54 is provided, for example, in the housing 42 and detects the temperature Tw of the coolant flowing through the refrigerant flow path 44. The temperatures T t and Tw detected by the temperature sensors 52 and 54 are input to the electronic control unit 40.
• the electronic control unit 40 controls the switching operation of the power transistors Q 1 and Q 2 of the DC—DC converter 32 and the voltage conversion ratio of the DC—DC comparator 32.
• Step-up ratio is controlled. Furthermore, the electronic control unit 40 controls the switching operation of the power transistor Q of the inverter 34 and controls the driving of the motor energy 38, and the power transistor Q 21 of the inverter 36 Control drive of motor generator 39 by controlling Q26. The details of the process in which the electronic control unit 40 controls the voltage conversion ratio of the DC-DC converter overnight 32 will be described below.
• a frequency setting unit 61 and a switching control unit 63 can be included.
• the carrier frequency setting unit 61 calculates the reference carrier frequency ⁇ c based on the temperature T t of the power transistors Q l and Q 2 detected by the temperature sensor 52 and the temperature Tw of the coolant detected by the temperature sensor 54. By setting, the switching frequency fc of power transistors Q l and Q 2 is set.
• the switching control unit 63 controls the duty ratio D of the switching control signal for driving the power transistors Q 1 and Q 2 on and off with the reference carrier frequency (switching frequency) fc set by the carrier frequency setting unit 61.
• DC Controls the voltage conversion ratio (step-up ratio) of the DC converter 32.
• the switching control signal where duty ratio D target duty ratio D 0 is established. Issue can be generated.
• the DC-DC converter 32 shown in Fig. 1 it is the ratio between the conduction period (Ql on) of the upper transistor Q1 and the conduction period (Q2 on) of the lower power transistor Q2.
• the voltage conversion ratio (step-up ratio) of converter 32 increases.
• FIGS. 5 and 6 are flowcharts for explaining processing in which the carrier frequency setting unit 61 of the electronic control unit 40 sets the reference carrier frequency (switching frequency of the power transistors Ql and Q2) fc
• FIG. 7 is a flowchart illustrating a process in which the switching control unit 63 of the electronic control unit 40 controls the output voltage of the DC-DC converter 32.
• the processes according to the flowcharts of FIGS. 5 to 7 are repeatedly executed at predetermined time intervals when the vehicle is turned on.
• step S 101 of the flowchart of FIG. 5 it is determined whether or not the value of the flag F 1 is zero. If the value of flag F1 is 0 (if the determination result in step S101 is YES), proceed to step S102, and if the value of flag F1 is not 0 (the determination result in step S101 is NO) ) Go to step S105. Note that the initial value of the flag F 1 when the ignition is turned on is set to 0.
• step S102 the power transistor Q l, detected by the temperature sensor 52 is detected. It is determined whether the temperature T t of Q 2 is equal to or lower than a threshold value. If the temperature T t of the power transistors Q 1 and Q2 is equal to or lower than the threshold value (if the judgment result in step S 102 is YES), the process proceeds to step S 103 where the reference carrier frequency fc is set to the high carrier frequency fh. The On the other hand, if power transistor Q 1 ⁇ temperature 32; higher than 32, is higher than the threshold (if the determination result in step S102 is NO), the process proceeds to step S104, where the reference carrier frequency fc is the high carrier frequency. It is set to a low carrier frequency f 1 (f Kf) lower than fh. In step S 105, the reference carrier frequency fc is fixed to the high carrier frequency fh, and the use of the low carrier frequency 1 is prohibited.
• the threshold used for the determination in step S102 can be made different when the reference carrier frequency fc is the low carrier frequency fI and when it is the high carrier frequency fh.
• the reference carrier frequency fc when the reference carrier frequency fc is the high carrier frequency fh, it is determined whether or not the temperature T t of the power transistors Q1 and Q2 is equal to or lower than the threshold value TO1, and the reference carrier frequency When the frequency fc is the low carrier frequency f 1, it can also be determined whether or not the temperature T t of the power transistors Q l and Q2 is equal to or lower than the threshold value TO 2 (TO 2 ⁇ T01).
• TO 2 ⁇ T01 the threshold value
• the reference carrier is the low carrier frequency f 1 and the temperature of the power transistors Q1 and 02 becomes 1 or less, the reference carrier frequency: fc is the low carrier frequency. Raised from 1 to high carrier frequency fh. As shown in Fig.
• step S201 of the flowchart of FIG. 6 it is determined whether or not the coolant temperature Tw detected by the temperature sensor 54 is equal to or lower than the set temperature T1.
• the flag F1 is set to 0.
• the process proceeds to step S203, and the value of the flag F1 is set to 1.
• the value when the value of the flag F 1 is 1 is set smaller than when the value of the flag F 1 is 0, It is possible to add hysteresis to the relationship between the coolant temperature Tw and the value of flag F1.
• the reference carrier frequency ⁇ c is set to the low carrier frequency f 1 when the temperature T t of the power transistors Q 1 and Q 2 exceeds the threshold.
• the coolant temperature Tw exceeds the set temperature T1
• the reference carrier frequency fc is set higher to the high carrier frequency fh.
• the carrier frequency setting characteristic determined by the power transistor Q l, ⁇ 32 temperature exactly 1 and the carrier frequency setting characteristic determined by the coolant temperature Tw are different.
• the power transistors Ql and Q2 generate heat, and the higher the switching frequency (reference carrier frequency) fc, the greater the amount of heat generated by power transistors Q1 and Q2.
• the reference carrier frequency fc is set low from the high carrier frequency fh to the low carrier frequency f 1.
• the frequency of the reference carrier switching frequency of power transistors Q1 and Q2
• the amount of heat generated by power-ranges Ql and Q2 will decrease, but the ripple of current flowing through reactor L and filter capacitor C1 will decrease. Components increase and the amount of heat generated by reactor L and filter capacitor C1 increases.
• the temperature rise characteristics of the power transistors Q l and Q2 and the temperature rise characteristics of the reactor L and the filter capacitor C 1 are opposite to the frequency change of the reference carrier.
• the frequency of the reference carrier is independent of the power transistor Q1, (32, regardless of the temperature. fc is set to the high carrier frequency fh, and the use of the low carrier frequency f 1 is prohibited, where the temperature T t of the power transistors Q l and Q 2 is the temperature Tw of the coolant and the transistor Q 1, It changes according to the current flowing through Q 2 and tends to increase as the coolant temperature Tw increases, and also increases as the current flowing through the power transistors Q l and Q 2 increases.
• the reactor L and the filter capacitor C 1 By fixing the reference carrier frequency fc to the high carrier frequency ⁇ h when the temperature is high (prohibiting the use of the low carrier frequency ⁇ 1), as shown in Fig. 9, the reactor L and fill capacitor C Since the ripple current flowing through 1 can be reduced, it is possible to suppress the temperature rise of the reactor L and the filter capacitor C 1.
• step S 3 0 1 in the flowchart of Fig. 7 the coolant temperature Tw detected by the temperature sensor 5 4 is equal to or lower than the set temperature ⁇ 2 (T 2> T 1). Determine whether or not Is done.
• step S302 If the coolant temperature Tw is equal to or lower than the set temperature T2 (if the judgment result in step S301 is YES), the process proceeds to step S302 and the output voltage of the DC-DC converter. 32 (smoothing capacitor C2 Voltage) The duty ratio D of the switching control signal to the transistor Ql, Q2 is controlled so that Vo ut becomes the predetermined target output voltage V 0 (V0> Vb, Vb is the voltage of the secondary battery 31) The step-up ratio of the DC—DC converter 32 is controlled. Next, in step S303, the value of the flag F2 is set to 0. On the other hand, when the temperature Tw of the coolant is higher than the set temperature T 2 (when the determination result in step S301 is NO), the process proceeds to step S304. Note that the initial value of flag F2 when idance is turned on is set to zero.
• step S 304 it is determined whether or not the coolant temperature Tw is equal to or lower than the set temperature T 3 (T 3> T 2). When the coolant temperature Tw is less than the set temperature ⁇ 3
• step S304 If the judgment result in step S304 is YES), the process proceeds to step S305, where the DC-DC comparator 32 is set to the target output voltage V 0 when the coolant temperature Tw is lower than the set temperature T2 In order to reduce the output voltage Vout, the duty ratio D of the switching control signal (DC—DC comparator step-up ratio 32) is limited.
• the output voltage Vo ut (step-up ratio) of the DC—DC converter 32 can be gradually reduced, and the DC-DC The output voltage Vo ut (step-up ratio) of the comparator 32 can be lowered step by step.
• step S 306 the value of the flag F 2 is set to 1.
• the coolant temperature Tw is higher than the set temperature T3 (when the determination result of step S304 is NO)
• the process proceeds to step S307.
• step S307 the switching operation of the power transistors Ql and Q2 is prohibited, so that boosting (voltage conversion) in the DC-DC converter 32 is prohibited.
• the power transistor Q 1 is kept on and the power transistor Q 2 ′ is kept off, so that the output voltage Vout of the DC-DC converter 32 becomes the input voltage of the DC-DC converter 32 (secondary battery 31 voltage) equal to Vb.
• step S308 the value of the flag F2 is set to 2. The value of flag F2 here is limited or prohibited from boosting the DC-DC converter 32.
• the DC temperature is less than when the coolant temperature Tw is less than the set temperature ⁇ 2.
• the duty ratio D of the switching control signal is limited so that the step-up ratio (voltage conversion ratio) of the DC converter 32 is lowered.
• the coolant temperature Tw when the coolant temperature Tw is higher than the set temperature T1, the process of fixing the reference carrier frequency fc to the carrier frequency fh is performed, and the coolant temperature Tw is set to the set temperature T. 2
• the duty ratio D step-up ratio
• the temperature rise of the reactor L and the fill capacitor C 1 can be suppressed also by performing one or more of these processes.
• the coolant temperature Tw when the coolant temperature Tw is higher than the set temperature T1, the reference carrier frequency fc is fixed to the high carrier frequency fh, and the coolant temperature Tw is set to the set temperature T2 (T2> T).
• the duty ratio D can be limited so that the output voltage Vout of the DC-DC converter 32 is lower than V0.
• the coolant temperature Tw when the coolant temperature Tw is higher than the set temperature T1, the reference carrier frequency fc is fixed to the high carrier frequency ⁇ h, and the coolant temperature Tw is set to the set temperature T 3 (T 3> T If it is higher than 1), the switching operation of the power transistors Q 1 and Q 2 can be prohibited.
• the duty ratio D is limited so that the output voltage Vout of the DC-DC converter 32 is lower than V0, and the coolant temperature Tw
• the coolant temperature Tw When the temperature is higher than the set temperature T3 (T 3> T 2), the power transistor Q 1 and Q 2 switching operation can be prohibited.
• the coolant temperature Tw when the coolant temperature Tw is higher than the set temperature ⁇ 1, only the process of fixing the reference carrier frequency fc to the high carrier frequency fh can be performed.
• the coolant temperature Tw is higher than the set temperature T2
• the coolant temperature Tw is higher than the set temperature T3
• only the process of prohibiting the switching operation of the power transistors Q1 and Q2 can be performed.
• the temperature of the filter capacitor C 1 detected by a temperature sensor (not shown) can be used.
• the configuration of the DC-DC converter 32 to which the present invention can be applied is not limited to the configuration shown in FIG. 1, and the present invention can also be applied to DC-DC converters having configurations other than those shown in FIG. Is possible.
• this invention is not limited to such embodiment at all, and can be implemented with a various form within the range which does not deviate from the summary of this invention. Of course.

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